It took 3 years, when the fix was not only on the roster the whole time but he had proven he could do it as a rookie in 2020. I know only one poster that will die defending that by saying Onwenu is a top 5 G in the league. He could be the best guard of all time and it's meaningless if the next spot is held by a turnstile. Much easier to find a functional RG (i.e. Sow) than RT.
As a rookie, Onwenu gave up 3 sacks, 1 hit, and 10 hurries on 616 snaps at RT.
As a 3rd year player, Onwenu gave up 1sack, 3 hits, and 11 hurries on 1044 snaps at RG.
Lowe was a "turnstile" because he's never played RT previously at the PRO-level. He didn't even take snaps there with Minnesota. He was strictly at LT.
Blame Belichick and Klemm for that decision. Lowe last played RT as a Freshman in 2017. He'd been at LT for 49 games and with Minny last year.
Calvin Anderson spent most of his career at LT to this point., Again, trying to plug him into RT was a mistake.
Putting Onwenu at RT should only be a temporary fix. It's not his best position. Getting someone to play LT should be the priority in the Off-season, but a competent swing tackle is needed as well, since Lowe clearly doesn't have what it takes for the right side yet.
I said before the season that the Pats should extend Onwenu and a bunch of people s**t on that idea. Yet, those same people are the ones saying to extend him now.